Saturday, August 30, 2008

Week TechVideo, 2008 #35 - Power Functions Steering Wheel

This week, one video from a model already referenced here at TBs , some time ago.
It is a spokeless LEGO steering wheel, which allows to drive remotely, LEGO PF vehicles (for instance, with rack & pinion steering or tracked with adder-subtractor gear train).




For more images from this creation, take a look at the respective webpage (in German).

It is a nice, very well done and imagined construction which should deliver lots of fun!

Friday, August 29, 2008

Going to all places, in all directions: the Killough platform

Regular wheeled or tracked vehicles have been with us for decades and, in some cases, even for centuries. They have undeniable qualities: simplicity, speed, reliability.

But what if we need more maneuverability? Nature has come up with a ubiquitous solution: legs. A legged vehicle, the current examples existing practically only in robotics research labs, can move in any direction. But using few legs makes balancing difficult, and many legs are hard to coordinate.

So, a possible compromise between these two means of locomotion is what is known as a Killough platform, named after its inventor.

Structurally, it consists of three wheels (or sets of wheels) arranged in a triangle or three-point star. Each wheel pushes its end of the star in a tangential direction in relation to the centre. In the next images, each primary color represents each wheel's possible motion.



By combining the action of two of the wheels, the vehicle will move in the direction of the stopped wheel. The secondary colours represent the resultant motion (called a “vector addition”) of the vehicle.



There's also the possibility of moving in directions perpendicular to these: for this purpose, all wheels move. One of the wheels moves in the same direction as the vehicle, and the other two combine their motions to go in the same direction.



If you turn all motors in the same direction, the vehicle will turn around itself.



So, even if we can only have each motor in forward/off/reverse, there are 14 possible “simple” (only moving or only rotating) directions a Killough platform can move!



If you turn on only one motor, there’s an additional 6 directions (moving and turning) the vehicle will go, and if you turn on two motors in different polarities, there are 6 other directions. That’s a grand total of 27 combinations, including stopped. Another way to reach this conclusion is to know that there are three motors, and each one has three possible states (forward, off, reverse), which gives 3 x 3 x 3 = 27. And what if you can also vary each motor’s speed? The number of combinations becomes almost infinite!

Since this kind of drive has three degrees of freedom (X, Y and rotation angle) and all of them are controllable, it is considered a "holonomic" drive. With other drives, like the first one at the Week TechVideo, 2008 #33 vehicles use or the one standard cars have, we can’t control X and Y independently of rotation.



Complicated? There’s no denying that! But here is a simpler explanation:

Basically, it's a fancy word meaning that the robot is movable in every possible direction and can spin in every direction.
A Killough platform is holonomic in a two dimensional world – it can move forwards, backwards, left and right - and combine them to go diagonally - all without turning it's body. And it can also spin around. Those are the only motions possible for an object that's stuck to a two-dimensional surface like the floor.
In a three dimensional world, a holonomic robot would have to be able to move up and down - and also roll sideways and pitch forwards and backwards. A helicopter is a holonomic machine in that sense.

Here is a great description of a Lego Killough platform:
http://staff.science.uva.nl/~leo/lego/killough.html

Wikipedia has a nice explanation of holonomic systems:
"In robotics holonomicity refers to the relationship between the controllable and total degrees of freedom of a given robot (or part thereof). If the controllable degrees of freedom is equal to the total degrees of freedom then the robot is said to be holonomic. If the controllable degrees of freedom is less than the total degrees of freedom it is non-holonomic. A robot is considered to be redundant if it has more controllable degrees of freedom than degrees of freedom in its task space. Holonomicity can be used to describe simple objects as well.
For example, a car is non-holonomic because although it could physically move laterally, there is no mechanism to control this movement.
A human arm, by contrast, is a holonomic, redundant system because it has 7 degrees of freedom (3 in the shoulder, 1 in the elbow and 3 in the wrist) and there are only 6 physical degrees of freedom in the task of placing the hand (x, y, z, roll, pitch and yaw), while fixing the 7 degrees of freedom fixes the hand."


This all sounds promising, but try building something like this using “regular” wheels and see what happens: a big problem appears!



The wheels will drag along the surface (indicated by the pink and light green arrows) when you the vehicle tries to move! This is where omniwheels (short for “omnidirectional wheels”) enter the show. They transmit torque from a motor in one direction like conventional wheels, but, unlike them, roll freely in the other direction. You’ll find below two types of omniwheel you can use in your vehicle.

So, what better way to know what Killough platforms can do than to look at some of them? There are numerous implementations made with LEGO, but my personal classics are those from Leo Dorst, Markus Matern (S, M and L), and Philippe “Philo” Hurbain. You can see the two different implementations of omniwheel employed: a pair of normal wheels arranged in a way that one of them is always touching the ground, and a wheel made of many tiny normal wheels on its rim.

On Markus’ Large Killough Platform page, there’s a nifty video that showcases this drive’s capabilities. First, the vehicle moves “the Killough way”: it moves in a square trajectory, without ever needing to change direction. Then, it goes through the same path, like a normal wheeled or tracked vehicle would do: goes straight, turns to face the new direction, and repeats the process. Much clumsier!

video


The Killough platform, being triangular in nature, is also an excellent application of the structures that were the spotlight of TBs TechTips 011. This is especially useful if you employ the studless construction method, like in the next video by RobotThoughts (which, by the way, doesn't feature any wheels at all):


Usually, each motor drives an omniwheel. This is mechanically simple, and easy for an RCX or an NXT to control. But what if you want to remotely control it yourself? You’d need to simultaneously coordinate directions and speeds for three motors! This is probably what Alexander Holroyd thought, so, just like controlling differential-drive vehicles (like the 8275 Bulldozer) can be simplified using a dual-differential drive (like the second example Conchas posted at Week TechVideo, 2008 #33), he built a mechanism to have one motor to control each degree of freedom . I was never very good at understanding differential-based mechanisms, and this one is definitely too much for me!



Yeah I know, all this stuff about vectors and directions and whatnot most certainly sounds complicated, and the mathematical concepts behind it surely can be; but don’t worry, since as soon as you build one of these and experiment yourself with it, you’ll quickly understand the important bits and be marvelled at what it can do. After all, isn’t learning by observation and experimentation exactly what TECHNIC is all about? Wink

Sunday, August 24, 2008

Week TechVideo, 2008 #34 - Lego Autonomous Underwater Vehicles

It is not one other LEGO underwater machine (probably will publish here about that one too, in the near future), recently shown at 'NI Week 2008' in Austin, Texas USA.
But something equally unexpected and amazing!

On the video below two AUVs (Autonomous Underwater Vehicles) performing amazingly.
One submersible and one line follower.




These were Polytechnic University's developed AUVs, shown at ASEE (American Society for Engineering Education) in 2007.
Each AUV here presented, was controlled by an RCX perfectly insulated, to operate underwater. In what concers LEGO motors, they
are not watertight but more like water resistant.

Do not submerge your motors at home, because there is an huge chance to damage them. If trying, you are doing it at your own risk!

Friday, August 22, 2008

Can you trace this part?

TBs reader Cagri (legoadam) from Turkey, has got a few TECHNIC links whose origin is not traceable anymore, but which are a bit different from the usual ones.
As you can see from the pictures below, these (on the left) do not have the barriers present in the regular 'TECHNIC, link 1x6' (on the right).
Their origin or the sets where they were included, etc... are uncertain.




The exemplars Cagri got are black which may restrict the possibilities to trace the original set(s).
They could be either an older part with an initial design which were modified after short time and make this part uncommon, or a new one.

Instead of barriers at one side and small protuberances on the other, these parts have little protuberances near top and bottom edges of the rings on both link ends. So you can't force a towball to pass through the holes.
The towball fits into the link just like the link with barriers. There is no difference except that you can make it fit on both sides unlike the link with barriers, as illustrated on the image below.



  • Have you ever seen this part, or can you help to locate it?
  • In which set(s) were they used?

It is not inventoried at BrickLink neither Peeron and unless we make further findings, it will be quite difficult to get this part added into parts database of the above mentioned tools.


Edit:
According to the testimonials from several of us, it was found that the older sets used inf fact the link version without barriers in black color, since 1988.
As examples we have the sets: 8855 (Prop Plane) and 8865 (Test Car).
It looks also that first exemplars of 8880 (Super Car) also used this version, which would extend the life span of this part former version till 1994, at least.

With these findings Cagri shouldn't have problems anymore, to get approval from BrickLink admins to get this part added into the database and hopefully the inventories from the affected sets will get corrected too.

Find all the gathered details, through the comments added to this post.


Last Update: 2008.Aug.23 00:29 GMT

Is it a new sort of TECHNIC beam?

Unfortunately the picture from this new Bionicle set for 2009 is quite out of focus, but I'm pretty sure we have here a new part to enlarge the TECHNIC inventory.
A new 'T' shaped 3x3 beam.
What do you think?

Click on the photo to display the larger and original picture.


If it is really a new part, it will be of great use among TECHNIC builders for sure.
Also it would the 2nd new part found after the new TECHNIC panel design present at 8264 (Transport or Dumper Truck), in yellow.


Edit:
Well, it seems it is in fact not a new part as someone raised in the comments section to this post.
Most likely it is a combined Bionicle chest 'panel' with a 'T' beam, like it is the case of Carapar from 2007.


Last Update: 2008.Aug.22 10:29 GMT

Wednesday, August 20, 2008

The first images from 1H2009 TECHNIC sets

Today the first images for the 2009 TECHNIC sets were published at lokosuperfluoLEGOman's BS folder.
These were taken from the retail catalog (January-May 2009), leaked in Spain.





So it seems that from the TECHNIC sets, on the rumored list published yesterday, we have:
  • 8260 - Mini Tractor / Tractor
  • 8261 - Monster Truck / Rally Truck
  • 8262 - Quad-Bike
  • 2H2009!? - Crane Truck
  • 2H2009!? - Mini Dozer / Bulldozer
  • 2H2009!? - Pisten Bully
  • 2H2009!? - Hauler
  • 2H2009!? - Wheel Loader

As news of today, we got:
  • 8256 - Super Kart
  • 8264 - Transport Truck or Dumper Truck
    This one got a PF Linear actuator and M-Motor, as well as new TECHNIC yellow panels in the style of the 2008 Bionicle ones.

These makes me think that 8258 and 8259 could become the new PF elements that will be sold individually, 8263 could be a new PF Kit for the 2nd half and the remaining 2nd half sets from 8265 onwards (most likely not more than three larger sets). Pure and not fundamented speculation...


And many other sets non TECHNIC, still waiting for the folder to be moderated (Ferrari [1], Indiana Jones [2, 3, 4], Star Wars [5, 6, 7, 8, 9]), but accessible through the respective deeplinks.

Tuesday, August 19, 2008

Rumors about new TECHNIC sets for 2009

The contents previously shown on this post were hidden, in answer to a kind request from Mr. Hung himself!
He claims the info to have been "stolen" from him, through cache manipulation and that not all the spread content may correspond to the 2009 sets to come.
He is also concerned with the damage this too early info may cause to TLG at this point.

I don't think these to be the case, but lets go this way at least until further info pops-up.
There are already some images available at BS from a 2009 consumer catalog, but unfortunately not yet from the TECHNIC or Racers supercars sets.


BR,
Fernando Correia

Monday, August 18, 2008

HiTechnic released new block to control PF motors

HiTechnic have released a new extended NXT MINDSTORMS programming block for their 'NXT IRLink Sensor', targeted for Power Functions control trough the LEGO IR Receiver.

The new 'Power Functions Extended IRLink Sensor Block for MINDSTORMS NXT Software' allows full speed and direction control for Power Functions motors with the IRLink.
This block provides features enabling the NXT program to control PF motor speed, direction and brake or coast mode.

Download the new block from HiTechnic downloads page.

New Isogawa LEGO TECHNIC Books

After having released,

  • the 'LEGO TECHNIC, LEGO MINDSTORMS' book




Isogawa Yoshihito published now, three new books to complement his collection of books. These illustrate many building techniques and examples of TECHNIC solutions, mechanisms, etc... that you may need to use at your own creations.
The original name in Japanese is "burotsuku de tsukuru kikai no hon" which translates into "How to build machines with bricks".




These are based on the PDF book "Tora no Maki", but got more examples with LEGO MINDSTORMS NXT motors and explanations were added to the previous edition with images only (although in Japanese).


The new books are,

  • Red Book (Rotation, transmission and various basic mechanisms)


  • Blue Book (Running, turning and various automobile mechanisms)


  • Green Book (Walkers, complex and various mechanisms)


You may find here, the several books contents in English and order them through this website.
Most of the images are self explanatory, so you don't need to care about the Japanese characters...

For a a larger review on these books, please refer to the original post at 'The NXT STEP" from Jim Kelly.

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